1. Field of the Invention
This invention relates to an apparatus for reproducing information recorded in an information recording carrier. Such an apparatus is preferably adapted to the information reproduction utilizing, e.g., optical means. In particular, this invention is directed to an information reproducing apparatus capable of always reproducing information data with accuracy.
2. Related Background Art
Recently, such information reproduction prevails as makes use of optical information recording carriers, such as optical files and compact discs. Further, these days such information reproduction begins to attract attention, which utilizes a card-like optical information reproducing carrier (hereinafter, referred to as an optical card) which has relatively excellent portability and large capacity.
In FIG. 1, an example of recording format for an optical card is schematically shown. On the optical card 1, a recording area 2 is formed, and in the recording area 2 a plurality of bands 3 are arranged. Each band 3 is formed by arranging a plurality of information tracks 4. Each track 4 has an information capacity of about several tens to a hundred bits. Each band 3 is separated from another one by a reference line 5 (hereinafter, referred to as R-line). An arrow A indicates a moving direction of the optical card 1 during the information reproduction, and an arrow C represents an information reading scan direction of an optical head during the same.
In FIG. 2, a reproducing apparatus is shown for reproducing the information recorded in such an optical card that has the record format as shown above. The optical card 1 is reciprocally movable along the direction A by a rotation device 6. The information recorded in the card 1 is read out to be reproduced by the head 11, track by track.
A light beam from a light source 7, such as an LED, is condensed by a lens system 8 to be projected onto the card 1. The information track 4 of the card 1 is imaged onto a linear sensor array 10 by an imaging optical system 9. The optical card 1 is moved in the direction A, so that correspondingly the image of information track 4 on the sensor array 10 changes. Plural read scannings are carried out in the sensor array 10 while each information track 4 is imaged on the sensor array 10. Thus, recorded information in some information tracks 4 belonging to a certain band 3 is exercised, and after completion thereof the optical head 11 is moved in the direction C by a proper distance in order to image the tracks 4 in another intended band 3 on the sensor array 10. Thus, the reproduction is similarly repeated.
FIG. 3 schematically illustrates an enlarged part of the record format of the optical card 1 as shown in FIG. 1. In this figure, a hatched portion corresponds to an information "1" or high level in the NRZI signal referred to later, and a blank one, an information "0" or low level in the same signal.
Such format as shown in FIG. 3 is that described in detail in U.S. Patent Appln. Ser. No. 904,359 (same assignee).
FIG. 3 shows one end portion of the record area 2 of the optical card 1, and therein a row of information bit arrangement in the direction C in an information track area 201 is the above-mentioned information track 4. A band area 203 consists of a R-line area 202 and the information track area 201. A unit data area 204 of the information track is formed of five bits. The information track is composed of a set of such unit data area. The R-line area 202 has a length of six bits in the direction C. Opposite bits of these six bits have the information "0" in the sense set forth above, and the other four bits have the information "1" in the above sense, which shape in stripe-like, i.e., the width in the direction A being shorter than that of one bit. Each stripe is disposed correspondingly to each information track.
The reading operation of the information track by the sensor array 10 is initiated upon detection of the information "011110" in the above sense, of the R-line area 202, judging that the alignment between the information track and the sensor array 10 is correctly achieved. Next, judging that the sensor array 10 is moved to next information track, by detecting again the information "011110" of this next information track after the information "011110" of the preceding R-line once disappears and then the information "000000" thereof is obtained, the same reading operation is effected. Such movement of the sensor array 10 to next information track is done by moving the optical card 1 relative to the optical head 11 in the direction A. In such manner, the R-line area 202 is an area not only for distinguishing each track from the adjacent track in the direction C but for distinguishing each track from the adjacent track in the direction A.
In order to reproduce the recorded information of the optical card 1 over plural band areas 203, the information tracks 4 in each band 3 are reproduced by moving the optical head 11 in the direction C. In this movement, it is necessary to control the position of the optical head 11 in such a manner that the image of the information track over all range of the intended band area 203 lies within the effective reading area of the sensor array 10. This control of the optical head's position is performed so as to position the R-line area 202 of the intended band within the predetermined range of the sensor array 10.
In the above reproduction system, the reproduced signal of the information is output only when the R-line is detected, and plural readings are conducted by the sensor array 10 per one information track according to the relationship between the relative moving velocity in the direction A of the card 1 and the reading scan velocity of the sensor array. Therefore, the firstly reproduced signal is generally caused to be the reproduced information of the concerned information track for each information track.
However, in the event that there are some flaws or dust on the optical card 1, or that a little defect is created in the information track area 201 during manufacture, it may occur that the above first reproduced signal does not accurately represent correct information.
Further, in the case that there are some defects or dust attached to the card or that the R-line is incorrectly formed, since the reproduced signal of the information is output only when the R-line is detected, the R-line could not be detected with the result that the information of the concerned track could not be reproduced and further that even the fact of the non-production of the concerned information track remains unknown.
Consequently, the serious problem often occurs that the reproduced information is inadequately corrected to produce incorrect information in the case where the error correction of the information in the optical card is done per one block consisting of plural information tracks. Moreover, in the case a lump of information is composed of a set of plural information tracks, such as a picture information track and a sound information track, in the recorded information of the optical card, the mal-synchronization of the picture, sound, and the like occurs owing to the information lacking.